Xref: utzoo comp.protocols.tcp-ip:11424 comp.dcom.lans:5079 Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!tut.cis.ohio-state.edu!rutgers!aramis.rutgers.edu!athos.rutgers.edu!hedrick From: hedrick@athos.rutgers.edu (Charles Hedrick) Newsgroups: comp.protocols.tcp-ip,comp.dcom.lans Subject: Re: When is an ethernet full? Message-ID: Date: 29 May 90 21:28:21 GMT References: <1141@cica.cica.indiana.edu> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 29 >When is an ethernet full? We have a campus backbone composed of a >chipcom 10 Mbs ethernet over broadband and a UB 5 Mbs ethernet over >broadband (buffered repeaters). The UB and chipcom networks are bridged >to form one logical networks. According to our Network General sniffer, >we constantly maintain about 10-15 percent utilization or (300 - 1000 >packets per second). How much more traffic can this network support >before performance falls off measurably? Any ideas? I'd like to see you get data with a bit more time resolution. It's a bit unusual for networks to run at 10-15% all the time, day and night. More typically, there's a long-term variation over the course of a day, with more traffic during the day than night, and short-term variation as people boot machines, transfer big files, or do other things that cause a short-term demand for bandwidth. If you're running at 10% 24 hours a day, this suggests either a very odd mix of users and applications, or that most of your bandwidth is going to broadcast packets produced by rwhod or things of that nature. I have heard of networks with a constant broadcast load of that sort. In that case, replacing some or all of your bridges with routers might be more useful than trying to increase the bandwidth. In general I'd expect a peak to average ratio of about 10 to 1. That is, if you are averaging 10% usage, you are probably using 100% during brief periods. So you're about at capacity. If your 10% is made up mostly of a continuous background of broadcast packets, this might not be the case. But if you've really got that much broadcast traffic, you've got other problems. Like your hosts are all spending significant CPU dealing with it. If your 10% represents the maxima of your peaks, rather than a true average, then you're probably in good shape and still have some room to grow.